Solid-state imaging device, method for driving the same, and imaging device

ABSTRACT

In a CMOS image sensor ( 10 ) including a pixel array unit ( 12 ) having pixels separately arranged in even-numbered pixel rows and odd-numbered pixel rows, a reading operation performed on odd pixels having a short accumulation time is performed in an exposure start portion of even pixels having a long accumulation time. By this, even when the even pixels are saturated and signal charges overflow from the even pixels, and therefore, part of the signal charges intrude into the odd pixels adjacent to the even pixels, an adverse effect of blooming due to the saturation of the even pixels to signals of the odd pixels is eliminated since the reading operation performed on the odd pixels has already been completed. The adverse effect due to the blooming to the low-sensitive signals is eliminated when a method for attaining a dynamic range by differentiating accumulation times between adjacent pixels is employed.

TECHNICAL FIELD

The present invention relates to solid-state imaging devices, methodsfor driving solid-state imaging devices, and imaging devices, andparticularly relates to a solid-state imaging device employing atechnique of wide dynamic range, a method for driving the solid-stateimaging device, and an imaging device employing the solid-state imagingdevice.

BACKGROUND ART

In solid-state imaging devices such as MOS (Metal Oxide Semiconductor)imaging devices, for example, a technique of differentiatingaccumulation times (exposure times) of individual pixels included in apixel array unit in which pixels including photoelectric conversionelements are two-dimensionally arranged in a matrix, obtaininghigh-sensitive signals and low-sensitive signals in accordance withlengths of the accumulation times, and combining the high-sensitivesignals and the low-sensitive signals so that a wide dynamic range isattained has been widely known.

As a technique for attaining the wide dynamic range, a technique ofperforming electronic shutter operations with shutter speeds differentbetween even-pixel rows and odd-pixel rows, setting accumulation timesdifferent between the even-pixel rows and the odd-pixel rows so thatsignals having different sensitivities are obtained, and combining thesignals having the different sensitivities using a signal processingsystem in a later stage has been proposed (refer to Japanese UnexaminedPatent Application Publication 2006-253876, for example).

DISCLOSURE OF INVENTION

In the related art disclosed in Japanese Unexamined Patent ApplicationPublication No. 2006-253876, the sensitivities should be proportional tothe accumulation times. However, in fact, the sensitivities may beshifted from proportional values by more than ranges of errors. Thisoccurs due to a reason described below. That is, when a photoelectricconversion element of a certain pixel is saturated, an optical chargewhich is further generated overflows from the photoelectric conversionelement and part of the optical charge intrudes into a photoelectricconversion element in an adjacent pixel. Accordingly, a signal having asensitivity in proportion to an accumulation time is not obtained in theadjacent pixel.

The phenomenon described above in which part of an optical charge whichoverflows from a photoelectric conversion element of a certain pixelintrudes into a photoelectric conversion element of an adjacent pixel isreferred to as blooming. In the case of the related art described above,since pixels having a long accumulation time and pixels having a shortaccumulation time are arranged in the even pixel rows and the odd pixelrows so as to be adjacent to each other, optical charges overflow fromphotoelectric conversion elements of the pixels having a longaccumulation time which are likely to be saturated, and the overflowingoptical charges intrude into photoelectric conversion elements of thepixels having a short accumulation time, and accordingly, amounts ofsignals of the pixels having a short accumulation time increase.Consequently, in the pixels having a short accumulation time,sensitivities are not proportional to the accumulation times, andtherefore, accuracy of signal processing for attaining a wide dynamicrange is degraded.

Accordingly, an object of the present invention is to provide asolid-state imaging device capable of eliminating adverse effects tolow-sensitive signals due to blooming when a wide dynamic range methodin which different accumulation times are employed between adjacentpixels is used, a method for driving the solid-state imaging device, andan imaging device.

In order to attain the object, according to the present invention, in asolid-state imaging device having a pixel array unit in which pixelswhich detect physical quantities are two-dimensionally arranged in amatrix and an imaging device employing the solid-state imaging device,physical quantities, which have been accumulated in a first accumulationtime (exposure time), of pixels in a first pixel group among the pixelsincluded in the pixel array unit are read, and physical quantities,which have been accumulated in a second accumulation time which isshorter than the first accumulation time, of pixels of a second pixelgroup which are arranged adjacent to the pixels of the first pixelgroup, among the pixels included in the pixel array unit are read in abeginning portion of the first accumulation time.

In the solid-state imaging device having the configuration describedabove and the imaging device, since the reading operation performed onthe pixels of the second pixel group having a short accumulation time isperformed in the beginning portion of the first accumulation time, thatis, in an exposure start portion of the pixels of the first pixel groupwhich have a long accumulation time and which are likely to besaturated, even when the pixels of the first pixel group are saturatedand the physical quantities overflow from the pixels, and therefore,part of the physical quantities intrude into the pixels of the secondpixel group which are arranged adjacent to the pixels of the first pixelgroup, signals output from the pixels of the second pixel group are notinfluenced by the physical quantities which have overflowed from thepixels of the first pixel group since the reading operation performed onthe pixels of the second pixel group has been completed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram schematically illustrating a system configuration ofa CMOS image sensor according to an embodiment of the present invention.

FIG. 2 is a circuit diagram illustrating an example of a circuitconfiguration of a unit pixel.

FIG. 3 is a diagram illustrating the relationships between electronicshutter scanning and scanning operations, i.e., odd-pixel reading andeven-pixel reading.

FIG. 4 is a diagram schematically illustrating electronic shutterscanning and read scanning according to the related art.

FIG. 5 is a diagram schematically illustrating the electronic shutterscanning and the read scanning according to the embodiment.

FIG. 6 is a block diagram illustrating an example of a configuration ofan imaging device according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will be described hereinafterwith reference to the accompanying drawings.

FIG. 1 is a diagram schematically illustrating a system configuration ofa solid-state imaging device according to the embodiment of the presentinvention. In this embodiment, a CMOS image sensor, for example, whichdetects, as a physical quantity, a charge amount in accordance with aquantity of visible light in a unit of pixel is taken as an example ofthe solid-state imaging device.

(Configuration of CMOS Image Sensor)

As shown in FIG. 1, a CMOS image sensor 10 of this embodiment has apixel array unit 12 in which unit pixels (unit sensors) 11 includingphotoelectric conversion elements which photoelectrically convertincoming visible light beams into charge amounts in accordance withquantities of the light beams are two-dimensionally arranged in a matrix(a form of a matrix).

In addition to the pixel array unit 12, the CMOS image sensor 10includes in its system configuration a vertical driving circuit 13,column signal processing circuits 14, a horizontal driving circuit 15, ahorizontal signal line 16, an output circuit 17, and a control circuit18, which serve as driving means for driving the pixels included in thepixel array unit 12, signal processing means for processing signalsoutput from the respective pixels, or controlling means for controllingthe system.

In this system configuration, the control circuit 18 externally receivesdata used to instruct an operation mode, for example, of the CMOS imagesensor 10, and externally outputs data including information on the CMOSimage sensor 10.

Furthermore, the control circuit 18 generates clock signals and controlsignals, for example, serving as references for operations performed bycircuits such as the vertical driving circuit 13, the column signalprocessing circuits 14, and the horizontal driving circuit 15, forexample, in accordance with a vertical synchronization signal Vsync, ahorizontal synchronization signal Hsync, and a master clock MCK. Theclock signals and the control signals, for example, generated by thecontrol circuit 18 are supplied to the vertical driving circuit 13, thecolumn signal processing circuits 14, and the horizontal driving circuit15, for example.

In the pixel array unit 12, the unit pixels (hereinafter simply referredto as “pixels” in some cases) 11 are two-dimensionally arranged in amatrix. As shown in FIG. 1, the unit pixels 11 are arrangedsubstantially in a square grid. This means that optical aperturesdefined by the photoelectric conversion elements and metal lines, forexample, are arranged substantially in a square grid. However, circuitportions of the unit pixels 11 are exceptions. That is, the circuitportions, which will be described hereinafter, of the unit pixels 11 arenot required to be arranged substantially in a square grid.

Furthermore, in the pixel array unit 12, pixel driving lines 19 areformed in a lateral direction of the drawing (a direction of arrangementof the pixels in pixel rows) for individual pixel rows in thearrangement of the matrix of the unit pixels 11, and vertical signallines 20 are formed in a vertical direction of the drawing (an directionof arrangement of the pixels in pixel columns) for individual pixelcolumns. First ends of the pixel driving lines 19 are connected tooutput terminals of the vertical driving circuit 13 corresponding to thepixel rows.

The vertical driving circuit 13 is constituted by a shift register andan address decoder, for example, performs selection scanningsuccessively on the unit pixels 11 of the pixel array unit 12 forindividual rows, and supplies required driving pulses (control pulses)to individual pixels in a selected one of the rows through the pixeldriving lines 19.

Here, assuming that, as shown in FIG. 1, in the pixel arrangement of thepixel array unit 12, pixels arranged in pixel rows to which odd numberssuch as 1, 3, and so on counted from the bottom are assigned and whichare driven by the vertical driving circuit 13 through the pixel drivinglines 19 are referred to as odd pixels whereas pixels arranged in pixelrows to which even numbers such as 2, 4, and so on are assigned andwhich are driven by the vertical driving circuit 13 through the pixeldriving lines 19 are referred to as even pixels, the odd pixels and theeven pixels are arranged as shown in the drawing.

Although a configuration of the vertical driving circuit 13 is not shownin detail, the vertical driving circuit 13 includes in its configurationa read-scanning system for performing the selection scanningsuccessively on the unit pixels 11 which read signals for individualrows, and a sweep-scanning system for performing sweep scanning in whichunnecessary charges are swept out (reset) from the photoelectricconversion elements of the unit pixels 11 in the rows which aresubjected to read scanning by the read-scanning system during a periodof time corresponding to a shutter speed before the read scanning isstarted.

A so-called electronic shutter operation is performed by sweeping out(resetting) the unnecessary charges by the sweep-scanning system.Hereinafter, the sweep-scanning system is referred to as anelectronic-shutter scanning system. Note that the electronic shutteroperation means an operation of discharging optical charges of thephotoelectric conversion elements and newly starting exposure (startingaccumulation of optical charges).

A signal read in a reading operation performed by the read-scanningsystem corresponds to a quantity of a light beam which is incident onafter a preceding reading operation or a preceding electronic shutteroperation is performed. Then, a period of time from a reading timing inthe preceding reading operation or a sweeping timing in the electronicshutter operation to a reading timing in a current reading operationcorresponds to an accumulation time (exposure time) of an optical chargeof one of the unit pixels 11.

Signals output from unit pixels 11 in a selected one of the rows aresupplied to the column signal processing circuits 14 through thevertical signal lines 20 arranged for individual pixel columns. Thecolumn signal processing circuits 14 are arranged for individual pixelcolumns of the pixel array unit 12, for example, that is, arranged so asto have the one-to-one relationships with the corresponding pixelcolumns.

The column signal processing circuits 14 receive signals individuallyoutput from the unit pixels 11 of the selected row for individual pixelcolumns of the pixel array unit 12, and perform signal processing suchas CDS (Correlated Double Sampling) or signal amplification on thesignals so as to remove fixed pattern noise which is unique to each ofthe pixels.

Note that, here, although a case where a configuration in which thecolumn signal processing circuits 14 are arranged so as to haveone-to-one relationships with the pixel columns is employed is taken asan example, the configuration is not limited to this. For example, aconfiguration in which a single column signal processing circuit 14 isarranged for a plurality of pixel columns (the vertical signal lines 20)so that the column signal processing circuit 14 is shared in atime-sharing manner among the plurality of pixel columns may beemployed.

Horizontal selection switches (not shown) are connected between outputstages of the column signal processing circuits 14 and the horizontalsignal line 16. Note that a configuration in which each of the columnsignal processing circuits 14 has an A/D (analog/digital) conversionfunction, in addition to the functions of the CDS and the signalamplification, for example, so as to allow a pixel signal which has beensubjected to the signal processing such as the CDS or the signalamplification to be output as a digital signal may be employed.

The horizontal driving circuit 15 is constituted by a sift register andan address decoder, for example, and successively outputs horizontalscanning pulses φH1 to φHx (x denotes the number of pixels in ahorizontal direction) to thereby successively select the column signalprocessing circuits 14. The horizontal scanning pulses φH1 to φHxsuccessively turn on the horizontal selection switches arranged in theoutput stages of the column signal processing circuits 14.

By successively turning on the horizontal selection switches in responseto the horizontal scanning pulses φH1 to φHx, the pixel signals whichhave been processed for individual pixel columns by the column signalprocessing circuits 14 are successively supplied to the horizontalsignal line 16.

The output circuit 17 performs various signal processing operations onthe pixel signals which are successively supplied from the individualcolumn signal processing circuits 14 through the horizontal signal line16 and outputs the pixel signals. As a detailed signal processingperformed by the output circuit 17, for example, only buffering may beperformed, or black-level control, variation correction for individualcolumns, signal amplification, color processing, and the like may beperformed before the buffering.

(Circuit Configuration of Unit Pixel)

FIG. 2 is a circuit diagram illustrating an example of a circuitconfiguration of one of the unit pixels 11. As shown in FIG. 2, each ofthe unit pixels 11 according to this circuit example is configured as apixel circuit including, in addition to a photoelectric conversionelement such as a photodiode 111, four transistors, i.e., a transfertransistor 112, a resetting transistor 113, an amplification transistor114, and a selection transistor 115.

Here, N-channel MOS transistors are used as the transistors 112 to 115,for example. Note that a combination of conductivity types of thetransfer transistor 112, the resetting transistor 113, the amplificationtransistor 114, and the selection transistor 115 is merely an example,and is not limited to the combination of these.

As the pixel driving lines 19, three driving lines, i.e., a transferline 191, a resetting line 192, and a selection line 193 are arranged incommon for unit pixels 11 in an identical pixel row. First ends of thetransfer line 191, the resetting line 192, and the selection line 193are connected to, for each pixel row, output terminals of the verticaldriving circuit 13 which correspond to the pixel row.

An anode of the photodiode 111 is connected to a negative side of apower source such as the ground, and the photodiode 111 performsphotoelectric conversion on received light so as to obtain an opticalcharge (photoelectron, herein) in accordance with a quantity (physicalquantity) of the light. A cathode of the photodiode 111 is electricallyconnected to a gate of the amplification transistor 114 through thetransfer transistor 112. A node 116 which is electrically connected tothe gate of the amplification transistor 114 is referred to as an FD(floating diffusion) section.

The transfer transistor 112 is connected between the cathode of thephotodiode 111 and the FD section 116, and is turned on when an activetransfer pulse φTRF of a high level (for example, a Vdd level)(hereinafter referred to as “High active”) is applied to the gatethrough the transfer line 191 so as to transfer the optical chargeobtained through the photoelectric conversion performed by thephotodiode 111 to the FD section 116.

A drain of the resetting transistor 113 is connected to a pixel powersource Vdd and a source of the resetting transistor 113 is connected tothe FD section 116. The resetting transistor 113 is turned on when aresetting pulse φRST of High active is applied to a gate through theresetting line 192, and resets the FD section 116 by discharging acharge of the FD section 116 to the pixel power source Vdd before thephotodiode 111 transfers a signal charge to the FD section 116.

A gate of the amplification transistor 114 is connected to the FDsection 116, and a drain of the amplification transistor 114 isconnected to the pixel power source Vdd. The amplification transistor114 outputs a potential of the FD section 116 which has been reset bythe resetting transistor 113 as a resetting level, and further outputs apotential of the FD section 116 after the signal charge is transferredby the transfer transistor 112 as a signal level.

A drain of the selection transistor 115 is connected, for example, to asource of the amplification transistor 114 and a source of the selectiontransistor 115 is connected to a corresponding one of the verticalsignal lines 20. The selection transistor 115 is turned on when aselection pulse φSEL of High active is applied to a gate through theselection line 193, and relays a signal output from the amplificationtransistor 114 in a state in which the unit pixel 11 is being selectedto the corresponding one of the vertical signal lines 20.

Note that a circuit configuration in which the selection transistor 115is connected between the pixel power source Vdd and the drain of theamplification transistor 114 may be employed.

Furthermore, each of the unit pixels 11 is not limited to a unit pixelhaving four transistors as the described configuration, and a unit pixelhaving three transistors in which the amplification transistor 114 andthe selection transistor 115 are integrated may be employed. Circuitconfigurations of the unit pixels 11 are not particularly specified.

(Characteristics of this Embodiment)

In the CMOS image sensor 10 having the foregoing configuration, in orderto attain a wide dynamic range, this embodiment is characterized by amethod for differentiating between an accumulation time for pixels towhich high-sensitive signals are supplied and an accumulation time forpixels to which low-sensitive signals are supplied and reading timingsof the pixels provided that the high sensitive signals and thelow-sensitive signals are to be supplied in accordance with length ofthe accumulation times.

Note that, in the CMOS image sensor 10 according to this embodiment, theunit pixels 11 included in the pixel array unit 12 are categorized intopixels to which the high-sensitive signals are to be supplied and pixelsto which the low-sensitive signals are to be supplied for individualpixel rows. For example, pixels (even pixels) in even-numbered pixelrows are determined as pixels in a first pixel group to which thehigh-sensitive signals are to be supplied, and pixels (odd pixels) inodd-numbered pixel rows are determined as pixels in a second pixel groupto which the low-sensitive signals are to be supplied.

In the related art disclosed in Japanese Unexamined Patent ApplicationPublication No. 2006-253876 described above, by performing electronicshutter operations with shutter speeds different between the even-pixelrows and the odd-pixel rows, accumulation times different between theeven-pixel rows and the odd-pixel rows are set, and in addition, byperforming operations of reading the low-sensitive signals in a laterstages of the accumulation time of the pixels to which thehigh-sensitive signals are to be supplied, the high-sensitive signalsand the low-sensitive signals are obtained.

On the other hand, this embodiment is characterized in that readscanning on the pixels to which the high-sensitive signals are to besupplied and read scanning on the pixels to which the low-sensitivesignals are to be supplied are separately performed, and theaccumulation time of the pixels to which the high-sensitive signals areto be supplied and the accumulation time of the pixels to which thelow-sensitive signals are to be supplied are differentiated from eachother in accordance with timings of the reading of the pixels to whichthe high-sensitive signals are to be supplied and timings of the readingof the pixels to which the low-sensitive signals are to be supplied,instead of in accordance with scanning timings of electronic shutterscanning.

More specifically, in the CMOS image sensor 10 according to thisembodiment, as shown in FIG. 3, the electronic shutter scanning isperformed successively on the individual pixel rows before the readscanning is performed, and thereafter, read scanning is separatelyperformed on the odd-pixel rows and the even-pixel rows (odd-pixelreading/even-pixel reading) whereby the accumulation time of theodd-pixel rows and the accumulation time of the even-pixel rows aredifferentiated from each other.

Note that the electronic shutter scanning and the read scanning arerealized by configurations described below. As described above, thevertical driving circuit 13 includes the read-scanning system and theelectronic-shutter scanning system (sweep-scanning system) in itsconfiguration.

In this vertical driving circuit 13, the electronic-shutter scanningsystem serving as electronic shutter driving means is constituted by theshift register, for example. The shift register successively outputselectronic shutter pulses from a first row on a row-by-row basis wherebya so-called rolling shutter operation (or a focal plane shutteroperation) in which shutter scanning is successively performed from thefirst row is performed.

On the other hand, the read-scanning system is constituted by two shiftregisters, i.e., a shift register for even-row scanning and a shiftregister for odd-row scanning, and alternately outputs even-row readingpulses and odd-row reading pulses from the corresponding shift registerswhereby the different pixel rows, specifically, the even-pixel rows andthe odd-pixel rows which are adjacent to each other are alternatelysubjected to a reading operation. Here, the two shift registerscorrespond to first driving means and second driving means.

Furthermore, the read-scanning system may be constituted by an addressdecoder so that the odd-row reading pulses are successively output tothe odd-pixel rows arranged every other row in a range from a first rowto a seventh row as shown in FIG. 5, and from the seventh row onwards,selection scanning is performed alternately on the odd-pixel rows andthe even-pixel rows, for example, on the seventh row, the second row, aninth row, the fourth row, an eleventh row, the sixth row, and so on inthis order, by specifying addresses by the address decoder. Here, theaddress decoder corresponds to the first driving means and the seconddriving means.

Note that a scanning start row N of zigzag scanning in which theodd-pixel rows and the even-pixel rows are alternately subjected toselection scanning is determined in accordance with an accumulation timeaH in which a horizontal period H of the even pixels which have the longaccumulation time is employed as a unit. That is, the scanning start rowN of the zigzag scanning is obtained by the following equation: N=a−1.In the foregoing example, since the accumulation time aH of the evenpixels is 8H, the scanning start row N of the zigzag scanningcorresponds to the seventh row. In a case where the accumulation time aHof the even pixels is 10H, the scanning start row N of the zigzagscanning corresponds to the ninth row, and the zigzag scanning isperformed from the ninth row onwards.

When the read scanning is performed as described above, image signalsare not read from the individual pixels and not output from the CMOSimage sensor 10 in an order corresponding to the pixel arrangement ofthe pixel array unit 12. Accordingly, an image memory such as a framememory is arranged in the signal processing system in the later stage sothat processing of rearranging the pixel signals in an ordercorresponding to the pixel arrangement is performed by controllingwriting of the pixel signals to and reading of the pixel signal from theimage memory.

As described above, first, the electronic shutter scanning is performed,and thereafter, the scanning operations, i.e., the odd-pixel reading andthe even-pixel reading are performed to thereby determine theaccumulation time of the odd-pixel rows and the accumulation time of theeven-pixel rows at timings of the odd-pixel reading and the even-pixelreading, respectively.

Specifically, a period from a timing of the electronic shutter scanningto a timing of reading of the odd pixels corresponds to the accumulationtime (second accumulation time) of the odd-pixel rows, and a period froma timing of the electronic shutter scanning to a timing of reading ofthe even pixels corresponds to the accumulation time (first accumulationtime) of the even-pixel rows.

(Effects of this Embodiment)

Next, effects of this embodiment will now be described with reference toFIGS. 4 and 5 while being compared with those of the related art. FIG. 4is a diagram schematically illustrating the electronic shutter scanningand the read scanning according to the related art. FIG. 5 is a diagramschematically illustrating the electronic shutter scanning and the readscanning according to the embodiment.

In FIGS. 4 and 5, axes of abscissa denote time for the electronicshutter scanning and the read scanning. Although the number of rows, forexample, is different from that of FIG. 3 for convenience ofexplanation, the principle is the same. In this embodiment (FIG. 5),odd-pixel read scanning is performed first, and thereafter, even-pixelread scanning is performed.

Note that, as for the accumulation time, for facilitating understanding,the accumulation time of the odd pixels is determined to be 2H (Hdenotes the horizontal period) and the accumulation time of the evenpixels is determined to be 8H, in the pixel arrangement of 14 rows×22columns.

<Case of Related Art>

First, a case of the related art will be described with reference toFIG. 4. The read scanning is successively performed on individual pixelrows while the odd-pixel rows and the even-pixel rows are notdistinguished from each other, that is, in an order of an odd-pixel row,an even-pixel row, an odd-pixel row, an even-pixel row, and so on. Then,scanning operations are performed in two systems, that is, a scanningoperation for the odd-pixel rows and a scanning operation for theeven-pixel rows for an electronic shutter, and an accumulation time ofthe odd-pixel rows and an accumulation time of the even-pixel rows arecontrolled at timings of the scanning operations in the two systems ofthe electronic shutter.

As described above, in the driving method in which the accumulation timeof the odd-pixel rows and the accumulation time of the even-pixel rowsare controlled at timings of operations of the electronic shutter, sincea reading operation performed on the odd pixels which has shortaccumulation time and to which low-sensitive signals are to be suppliedis performed in a later stage of the long accumulation time of the evenpixels to which high-sensitive signals are to be supplied, in a casewhere the photodiode 111 is saturated when a period of timecorresponding to approximately 4H, for example, has passed after anexposure start time in the even pixels having the long accumulation timewhich are likely to be saturated, a defect described below occurs.

Specifically, in the saturated even pixels having the long accumulationtime, if optical charges overflow from the photodiodes 111 due toincident light which is further incident on, blooming in which part ofthe optical charges of the overflowing light intrudes the odd pixels inpixel rows (that is, the odd pixels having the short accumulation time)adjacent to a pixel row including the even pixels of interest occurs.When the blooming occurs, amounts of charges of the odd pixels becomelarger than amounts of the proper charges in accordance with an amountof the incident light by amounts of the optical charges which have beenintruded from the even pixels.

Accordingly, in the odd pixels having the short accumulation time, sincea reading operation has not yet been performed when the blooming occurs,and therefore, the proportional relationship between a sensitivity andthe accumulation time is no longer established after the part of theoptical charges overflowing from the even pixels adjacent to the oddpixels of interest intrude, signals in proportion to the accumulationtime are not output from the odd pixels.

Note that, here, for facilitating understanding, the description is madetaking the case where the blooming in which the part of the opticalcharges which overflow from the saturated pixels intrude to theindividual odd pixels in the pixel rows adjacent to the pixel rowincluding the saturated pixels (saturated even pixels) occurs in thepixel arrangement of 14 rows×22 columns as an example. However, theblooming may occur practically in individual odd pixels in the pixelrows which is arranged far from the pixel rows including the saturatedpixels by odd-numbered rows more than three rows in a pixel arrangementincluding a number of pixels which conform to various graphic displaystandards, that is, in the pixel arrangement including a number ofpixels.

As described above, if the odd pixels which should output thelow-sensitive signals do not output signals in proportion to theaccumulation time due to the blooming caused by the saturated pixels,the signals output from the odd pixels (low-sensitive signals) are notaccurate signals obtained in accordance with amounts of incident lightbeams. Accordingly, accuracy of the signal processing performed in thesignal processing system in the later stage for attaining a wide dynamicrange by combining the high-sensitive signals and the los-sensitivesignals is degraded.

<Case of this Embodiment>

Next, a case of this embodiment will be described with reference to FIG.5. Before the read scanning, the electronic shutter scanning isperformed successively on individual pixel rows, and thereafter, theread scanning is performed on the odd pixels having the shortaccumulation time and the read scanning is performed on the even pixelshaving the long accumulation time whereby, as is apparent from FIG. 5,an exposure period of the odd pixels (a period in which the opticalcharges are accumulated) corresponds to an exposure start portion (abeginning portion of the exposure start) of the even pixels.

As described above, the exposure period of the odd pixels corresponds toan exposure start portion of the even pixels. Therefore, even if thephotodiodes 111 in the even pixels which are likely to be saturated aresaturated after a period of approximately 4H, for example, has passedfrom the exposure start time, the optical charges start overflowing fromthe photodiodes 111 due to incident light beams which are furtherincident on, and part of the optical charges intrude into the odd pixelshaving the short accumulation time adjacent to the even pixels ofinterest, signals of the odd pixels which have been output are accuratesignals, that is, proper signals having signal levels corresponding toamounts of the incident light beams since the reading of the odd pixelshaving the short accumulation time has been terminated before theoptical charges overflow.

Specifically, taking the even pixels of the second row of FIG. 5 asexamples, even if the photodiodes 111 are saturated when approximately4H has passed from the exposure start time of the even pixels ofinterest and the optical charges start overflowing from the photodiodes111, after 1H has passed from the exposure start time of the even pixelsin a case of the odd pixels in the first row adjacent to the even pixelsin the second row, and on the other hand, after 3H has passed from theexposure start time of the even pixels in a case of the odd pixels inthe third row adjacent to the even pixels in the second row, that is,before the optical charges overflow from the even pixels in both cases,the reading operation is terminated.

Accordingly, the low-sensitive signals of the odd pixels in the firstand third rows adjacent to the even pixels in the second row are notadversely influenced by the optical charges which have overflowed fromthe even pixels. The same holds true for the odd pixels in the pixelrows arranged far from the pixel row including the saturated pixels byodd-numbered row more than three rows, as well as the odd pixels in thefirst and third rows.

Note that, part of the optical charges which have overflowed from theeven pixels (saturated pixels) in the second row and which have intrudedto the odd pixels in the first and third rows are swept away by the nextelectronic shutter operation, and therefore, are not adversely affectthe signals of the odd pixels of interest in the next field.

As described above, when the driving method in which the accumulationtime of the odd-pixel rows and the accumulation time of the even-pixelrows are controlled at timings of the odd-pixel reading operation andthe even-pixel reading operation is employed, even if the pixels havingthe long accumulation time and the pixels having the short accumulationtime are adjacent to each other, since the reading operation performedon the odd pixels having the short accumulation time has already beenterminated before the photodiodes 111 of the even pixels having the longaccumulation time are saturated and the optical charges startoverflowing, and therefore, the proportional relationship between thesensitivity and the accumulation time of the odd pixels is maintained atthe time of reading, low-sensitive signals in proportion to theaccumulation time are output from the odd pixels.

Note that in the even pixels which are likely to be saturated, a casewhere the photodiodes 111 are saturated within approximately 2H from theexposure start time and part of the optical charges start overflowingfrom the photodiodes 111 corresponds to a case where the photodiodes 111included in the odd pixels adjacent to the even pixels of interest havealready been saturated due to incident light of themselves and amountsof signals are unknown. Therefore, it is not necessary to take such acase into consideration.

As described above, in the CMOS image sensor 10 having the pixel arrayunit 12 in which the pixels in the first pixel group in which signalcharges are accumulated in the first accumulation time and the pixels inthe second pixel group in which signal charges are accumulated in thesecond accumulation time which is shorter than the first accumulationtime are separately arranged in the even-pixel rows and the odd-pixelrows, for example, in a unit of pixel row, even when the even pixels aresaturated and the signal charges overflow from the even pixels ofinterest and part of the signal charges intrude into the odd pixelsadjacent to the even pixels, by performing reading of the odd pixelshaving the short accumulation time (second accumulation time) in abeginning portion of the first accumulation time, that is, in a portionof the exposure start time of the even pixels having the longaccumulation time (first accumulation time), an adverse effect of theblooming generated when the even pixels are saturated to signals of theodd pixels are eliminated since the reading operation performed on theodd pixels has been terminated.

In the technique of attaining a wide dynamic range described aboveaccording to the present invention, since the reading operation isperformed only once for individual pixels for capturing an image havinga long accumulation time and a short accumulation time, even when readscanning is performed on two pixel rows, speed of the read scanning isnot changed. Accordingly, another technique of attaining a wide dynamicrange may be used in combination.

Furthermore, in the foregoing embodiment, although the unit pixels 11included in the pixel array unit 12 are categorized into the two pixelgroups of two levels of sensitivity, that is, a low sensitivity and ahigh sensitivity, the present invention is not limited to this. The unitpixels 11 may be categorized into three or more pixel groups of three ormore levels of sensitivity. For example, in a case where the unit pixels11 are categorized into three pixel groups of three levels ofsensitivity, i.e., a low sensitivity, a middle sensitivity, and a highsensitivity, the technique of attaining a wide dynamic range accordingto the present invention is applied between the pixel group of the lowsensitivity and the pixel group of the middle sensitivity and betweenthe pixel group of the middle sensitivity and the pixel group of thehigh sensitivity.

Note that, in the embodiment described above, the description is madetaking the case of the CMOS image sensor in which the unit pixels 11which detect signal charges corresponding to amounts of visible lightbeams as physical quantities are arranged in a matrix as an example.However, the present invention is applicable not only the CMOS imagesensor but also general image sensors which attain a wide dynamic rangein which accumulation times of adjacent pixels are differentiated.

Furthermore, the present invention is applicable to not only imagesensors in which a distribution of quantities of incident visible lightbeams is detected so as to be captured as an image, but also imagesensors in which a distribution of quantities of infrared rays, X-rays,or particles, for example, is captured as an image, general solid-stateimaging devices (physical-quantity distribution detection devices), suchas a fingerprint detection sensor, in which a distribution of otherphysical quantities, such as pressures or capacitances in the broadsense is detected so as to be captured as an image.

Moreover, the present invention is also applicable to not onlysolid-state imaging devices in which pixels in a pixel array unit aresuccessively scanned on a row-by-row basis so that signals are read fromthe pixels but also solid-state imaging devices of X-Y address type inwhich arbitrary pixels are selected on a pixel-by-pixel basis andsignals are read from the selected pixels on a pixel-by-pixel basis.

When a wide dynamic range method is employed in general solid-stateimaging devices including the solid-state imaging devices of X-Y addresstype, in a pixel array unit in which pixels which detect physicalquantities are two-dimensionally arranged in a matrix, among the pixelsincluded in the pixel array unit, physical quantities of pixels of afirst pixel group which are accumulated in a first accumulation time areread, and in addition, physical quantities of pixels, which are arrangedadjacent to the pixels of the first pixel group, of a second pixel groupwhich are accumulated in a second accumulation time which is shorterthan the first accumulation time are read in a beginning portion of thefirst accumulation time. Accordingly, since a reading operationperformed on the pixels of the second pixel group has already beenterminated when the pixels of the first pixel group are saturated, anadverse effect of blooming caused by the saturation of the pixels of thefirst pixel group to signals (low-sensitive signals) of the pixels ofthe second pixel group may be eliminated.

Not that such a solid-state imaging device may be formed as one chip oras a module form which has an imaging function and in which an imagingunit and one of a signal processing unit and an optical system areintegrally packaged.

Furthermore, the present invention is applicable to not only thesolid-state imaging devices but also imaging devices. Here, the imagingdevices include camera systems, such as digital still cameras and videocameras, and electronic devices having imaging functions, such ascellular phones. Note that the module form which is mounted on theelectronic devices, that is, a camera module may be included in theimaging devices.

[Imaging Device]

FIG. 6 is a block diagram illustrating an example of a configuration ofan imaging device according to the present invention. As shown in FIG.6, the imaging device according to the present invention includes anoptical system including a lens group 31, a solid-state imaging device32, a DSP (Digital Signal Processor) circuit 33 serving as a camerasignal processing circuit, a frame memory 34, a display device 35, arecording device 36, an operation system 37, and a power supply system38. The DSP circuit 33, the frame memory 34, the display device 35, therecording device 36, the operation system 37, and the power supplysystem 38 are connected to one another through a bus line 39.

The lens group 31 receives incident light beams (image light beams) froman object and forms an image on an imaging plane of the solid-stateimaging device 32. The solid-state imaging device 32 converts lightquantities of the incident light beams which are used to form the imageon the imaging plane by the lens group 31 into electric signals forindividual pixels and outputs the electric signals as pixel signals. TheCMOS image sensor 10 according to the embodiment described above is usedas the solid-state imaging device 32.

An order of the pixel signals output from the CMOS image sensor 10serving as the solid-state imaging device 32 does not corresponds to anorder of the pixel arrangement of the pixel array unit 12 shown in FIG.1, as described above, but corresponds to an order of the read scanningin the technique of attaining a wide dynamic range according to thepresent invention.

The DSP circuit 33 performs various signal processing operations on thepixel signals output from the solid-state imaging device 32. As anexample of the operations, the pixel signals output from the solid-stateimaging device 32 in an order in accordance with the read scanning inthe technique of attaining a wide dynamic range according to the presentinvention are controlled to be written into the frame memory 34 in anorder corresponding to the pixel arrangement of the pixel array unit 12,and the frame memory 34 reads the pixel signals in the ordercorresponding to the pixel arrangement of the pixel array unit 12.

The DSP circuit 33 further performs signal processing in which pixelsignals of even pixels having a long accumulation time and pixel signalsof odd pixels having a short accumulation time are combined so as toobtain an image which has an excellent image gradation (levels ofbrightness), that is, an image having a wide dynamic range, taking arate of the accumulation times into consideration. In addition to suchsignal processing, the DSP circuit 33 performs various known camerasignal processing operations.

The display device 35 which is a panel display device such as a liquidcrystal display device or an organic EL (Electro Luminescence) displaydevice displays moving images or still images captured by thesolid-state imaging device 32. The recording device 36 records themoving images or the still images captured by the solid-state imagingdevice 32 in a recording medium such as a video tape or a DVD (DigitalVersatile Disk).

The operation system 37 issues operation instructions on variousfunctions included in the imaging device during an operation conductedby a user. The power supply system 38 properly supplies various powersources serving as operation power sources of the DSP circuit 33, theframe memory 34, the display device 35, the recording device 36, and theoperation system 37 to these objects of supply.

As described above, when the CMOS image sensor 10 according to theforegoing embodiment is used as the solid-state imaging device 32 in animaging device such as a video camera, digital still camera, and acamera module for a mobile device such as a cellular phone, since anadverse effect of blooming caused by saturation of pixels having a longaccumulation time to which high-sensitive signals are to be supplied topixel signals having a short accumulation time (low-sensitive signals)is eliminated in the CMOS image sensor 10, high-accuracy signalprocessing is performed in the DSP circuit 33 for attaining a widedynamic range, and accordingly, quality of an captured image isimproved.

According to the present invention, when a method for attaining a widedynamic range by differentiating accumulation times of adjacent pixelsis employed, since a reading operation performed on pixels in a secondpixel group which have a short accumulation time is performed in anexposure start portion of pixels of a first pixel group which have along accumulation time, even when the pixels of the first pixel groupare saturated and physical quantities intrude into the pixels of thesecond pixel group, an adverse effect of blooming caused by thesaturation of the pixels of the first pixel group to signals(low-sensitive signals) of the pixels of the second pixel group may beeliminated since the reading operation performed on the pixels of thesecond pixel group has already been terminated by this time.

1. A solid-state imaging device characterized by comprising: a pixelarray unit in which pixels which detect physical quantities aretwo-dimensionally arranged in a matrix; first driving means for readingphysical quantities, which have been accumulated in a first accumulationtime, of pixels of a first pixel group among the pixels included in thepixel array unit; and second driving means for reading physicalquantities, which have been accumulated in a second accumulation timewhich is shorter than the first accumulation time, of pixels of a secondpixel group which are arranged adjacent to the pixels of the first pixelgroup among the pixels included in the pixel array unit, in a beginningportion of the first accumulation time.
 2. The solid-state imagingdevice according to claim 1 characterized in that, the pixels of thefirst pixel group and the pixels of the second pixel group are arrangedin a unit of a pixel row of the pixel array unit, and the second drivingmeans performs read scanning on the pixels of the second pixel groupbefore the first driving means performs read scanning on the pixels ofthe first pixel group.
 3. The solid-state imaging device according toclaim 2 characterized in that, the pixels of the first pixel group andthe pixels of the second pixel group are separately arranged ineven-numbered pixel rows and odd-numbered pixel rows in the pixel arrayunit.
 4. The solid-state imaging device according to claim 3characterized by comprising: electronic-shutter driving means forperforming an electronic shutter operation in which the pixel rows ofthe pixel array unit are successively scanned and the physicalquantities of the pixels are discharged from individual pixel rows,wherein the first driving means reads the physical quantities of thepixels of the first pixel group in synchronization with the electronicshutter operation at a timing in which the first accumulation time haspassed after the electronic shutter operation is performed, and thesecond driving means reads the physical quantities of the pixels of thesecond pixel group in synchronization with the electronic shutteroperation at a timing in which the second accumulation time has passedafter the electronic shutter operation is performed.
 5. A method fordriving a solid-state imaging device, characterized by: reading physicalquantities, which have been accumulated in a first accumulation time, ofpixels in a first pixel group among pixels which detect physicalquantities and which are two-dimensionally arranged in a matrix in apixel array unit; and reading physical quantities, which have beenaccumulated in a second accumulation time which is shorter than thefirst accumulation time, of pixels of a second pixel group which arearranged adjacent to the pixels of the first pixel group, among thepixels included in the pixel array unit, in a beginning portion of thefirst accumulation time.
 6. An imaging device characterized bycomprising: a pixel array unit in which pixels which detect physicalquantities are two-dimensionally arranged in a matrix; first drivingmeans for reading physical quantities, which have been accumulated in afirst accumulation time, of pixels of a first pixel group among thepixels included in the pixel array unit; second driving means forreading physical quantities, which have been accumulated in a secondaccumulation time which is shorter than the first accumulation time, ofpixels of a second pixel group which are adjacent to the pixels of thefirst pixel group, among the pixels included in the pixel array unit, ina beginning portion of the first accumulation time; and signalprocessing means for attaining a wide dynamic range by combining signalsobtained from the pixels of the first pixel group and signals obtainedfrom the pixels of the second pixel group.